Learning Disabilities Association of America
The LDA’s Healthy Children Project is dedicated to reducing the effects of environmental contaminants on brain development, especially in children. A growing body of research indicates that many learning and behavior problems are linked to toxic chemicals which are widespread in the environment and products, and to which we are exposed on a daily basis.
The Learning Disabilities Association created the Healthy Children Project to:
- Raise awareness of environmental factors, particularly toxic chemicals, that can harm brain development, contributing to learning disabilities and behavior disorders,
- Prevent toxic chemical exposures, especially among pregnant women and children,
- Build a nationwide network of LDA members working to protect children’s health and reduce the incidence of learning disabilities in future generations. LEARN MORE HERE…
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A Neurodevelopmental Perspective:
Why chemical safety statutes need to explicitly require that chemicals be found safe for the developing fetus and children
The Brain During Fetal Development and Early Childhood:
Critical Windows of Development
New research in the neurosciences is identifying “critical windows of vulnerability” during fetal development and early childhood. During these windows of development, toxic chemical exposures can cause lasting harm to the brain and nervous system. These windows exist only in early brain development; they have no counterpart in adult life.
Cellular Events in Neurodevelopment
Cell division, migration, differentiation, synapse formation, synapse pruning, and apoptosis (cell death) occur during brain development. This sequence is influenced by interactions among inherited genes and the environment. Each of these kinds of events is subject to disruption by environmental agents, including toxic chemicals. Some chemicals can disrupt more than one process. Interference with any stage of this process may alter subsequent stages and result in permanent impairments.
Thyroid Levels During Fetal Development
A healthy thyroid and normal thyroid hormone levels in pregnant women and later in infants and children are essential for healthy brain development. Even “subclinical hypothyroidism” – insufficient levels of thyroid hormones in the absence of apparent symptoms - in pregnant women can result in children with lower IQs, attention deficits, motor impairments and trouble with visual processing.
Chemicals that disrupt endocrine system function are called endocrine disruptors. Among them are chemicals that can disrupt normal thyroid function in a variety of ways. These chemicals also can interfere with some of the cellular events of brain development, including cell differentiation, migration, and growth of neurons.
Chemicals Harmful to Neurodevelopment:
“Top Ten” Worst Chemicals for Brain Development
According to a 2012 article by Drs. Landrigan, Lambertini and Birnbaum, the following are the top 10 chemicals and categories of chemicals widely distributed in the environment and already suspected of causing problems with brain development.[i]
- Polychlorinated Biphenyls (PCBs)
- Organophosphate pesticides
- Organochlorine pesticides
- Automotive exhaust
- Endocrine Disruptors*
- Polycyclic aromatic hydrocarbons
- Brominated flame retardants
- Perfluorinated compounds (used in non-stick and stain-resistant products)
Six of these chemicals/chemical categories are subject to the Toxic Substances Control Act: lead, methylmercury, PCBs, endocrine disruptors (other than pesticides), brominated flame retardants and perfluorinated compounds.
*Endocrine Disrupting Chemicals: Polychlorinated biphenyls, PBDEs, perfluorinated compounds and bisphenol A are examples of EDCs. These chemicals are also all thyroid disruptors.
Majority of Chemicals Untested for Neurodevelopmental Toxicity
While a great deal of scientific evidence shows that the “top 10” chemicals are toxic to the developing human brain, the vast majority of chemicals remain untested for neurodevelopmental effects. Of the roughly 80,000 industrial chemicals on the market, about 1000 are known to be neurotoxic in laboratory studies; 200 are known to be neurotoxic to adult humans; about a dozen are known to harm brain development.
Children’s Exposures to Toxic Chemicals:
Low-Level Exposures Harmful
Some toxic chemicals can harm the developing brain at extremely low levels – in some cases the lowest levels detectable. These levels are far below those that can harm adults. These low-level exposures are linked to lost intelligence, shortened attention and disrupted behavior.
American babies are born with as many as 200 synthetic chemicals in their bodies, as shown in analyses of cord blood.[ii] These chemicals include many of the neurodevelopmental toxicants listed above. A 2011 analysis of the U.S. CDC’s biomonitoring data (NHANES data) found that at least 90 percent of pregnant women have detectable levels of 163 industrial chemicals in their bodies, including BPA, phthalates, PBDEs, perfluorinated compounds, PCBs, lead and mercury.[iii]
Per pound of body weight, children breathe more air, eat more foods and drink more fluids than adults. They spend more time on the ground where dust and chemicals accumulate, and put hands and objects in their mouths. The US CDC’s NHANES data consistently show that young children have higher levels of certain chemicals in their bodies than adults.
Children are uniquely vulnerable to harm from toxic chemical exposures because of their biology, metabolism and behaviors. Recent science shows that beginning in the womb, children are more highly exposed to toxic chemicals, and that these exposures, even at extremely low levels, can do lasting harm, resulting in learning or developmental disabilities.
[i] Landrigan P, et al. A research strategy to discover the environmental causes of autism and neurodevelopmental disabilities. Environmental Health Perspectives [Internet]. 2012 [cited 2012 April 25];120:a258-a260. Available from: http://dx.doi.org/10.1289/ehp.1104285.
[ii] Environmental Working Group. Pollution in People: Cord Blood Contaminants in Minority Newborns. 2009 http://www.ewg.org/minoritycordblood/BPA-cordbloodpollution
[iii] Woodruff T, et al. Environmental chemicals in pregnant women in the United States. Environmental Health Perspectives. 2011 June; 119(6):878-885.
Published online 2011 January 14. doi: 10.1289/ehp.1002727
This document is informed throughout by the work of Ted Schettler, M.D., Science Director, Science and Environmental Health Network; and Philip J. Landrigan, M.D., Dean of Global Health and Professor of Pediatrics, Mount Sinai School of Medicine.